E85 fuel composition and method

ABSTRACT

An E85 fuel composition comprising ethanol, gasoline and isopentane present in amounts so that the fuel meets the applicable minimum vapor pressure limits of ASTM D 5798 is disclosed. A method for producing an E85 fuel composition comprising adding a sufficient quantity of isopentane to ethanol or a mixture of ethanol and gasoline which has a vapor pressure lower than an applicable minimum vapor pressure limit of ASTM D 5798 to produce an E85 fuel having a vapor pressure that complies with the applicable minimum vapor pressure limits of ASTM D 5798 is also disclosed.

FIELD OF THE INVENTION

The present invention relates to fuels, particularly ethanol fuels,which contain gasoline and which comply with the ASTM D 5798 and whichare suitable for use in California.

BACKGROUND OF THE INVENTION

Environmental and energy independence concerns have stimulated thedevelopment of alternative transportation fuels, such as alcohol fuels,for use in automobiles. Alcohol fuels include methanol and ethanol.Alcohol in the form of ethanol is combined in various percentages withgasoline to produce one type of alternative fuel. Ethanol in the form ofE85 (i.e., 85 vol % ethanol and 15 vol % gasoline) is an example of atype of alcohol mixed with gasoline to produce an alternative fuel.

There has been increased interest in E85 by the State of California andother states. E85 fuel formulations must be in compliance withapplicable regulations, which in California would include meeting thevapor pressure minimum limits set forth in ASTM D 5798. Specification D5798 has three volatility classes (1, 2, and 3) with minimum vaporpressures of 5.5, 7.0, and 9.5 psi which are assigned based on theexpected minimum ambient temperature where they will be marketed.California requires Class 1 in the summertime, Class 2 in the spring andfall (and some areas during winter), and Class 3 is required in someareas in November, December, and January.

Minimum vapor pressures are specified to ensure good cold starting andwarm-up drivability. Simply blending commercially available gasolinemeeting local volatility requirements with ethanol does not result in afuel that meets the minimum vapor pressure limits of ASTM D 5798. Thus,there is a need for an E85 fuel formulation that meets the ASTM D 5798specifications and a method for producing the E85 fuel.

SUMMARY OF THE INVENTION

Among other things, the present invention provides, an E85 fuelcomposition comprising ethanol, gasoline and isopentane present inamounts so that the fuel meets the applicable minimum vapor pressurelimits of ASTM D 5798. The present invention also provides a method forproducing an E85 fuel composition by adding a sufficient quantity ofisopentane to ethanol or a mixture of ethanol and gasoline which has avapor pressure lower than an applicable minimum vapor pressure limit ofASTM D 5798 to produce an E85 fuel having a vapor pressure that complieswith the applicable minimum vapor pressure limits of ASTM D 5798.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a bar graph showing the effect of gasoline vapor pressure onthe vapor pressure of the finished E85 blend.

FIG. 2 is a graph showing the effect of base fuel vapor pressure andisopentane content on the vapor pressure of the finished E85 blend.

FIG. 3 is a graph showing the correlation between predicted and actualvapor pressures.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following description of the preferred embodiment(s) is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. The diagrams and discussion refer generally toethanol and specifically to an ethanol fuel in the form of E85 (i.e.,85% ethanol and 15% gasoline) as a type of alcohol mixed with gasolineto produce an alternative fuel. This is not intended as a limitationhowever, as it should be apparent to one skilled in the art that thepresent invention would equally apply to other alternative fuels andother combinations of ethanol and gasoline, such as E70.

The term E85 as used herein is not limited to a fuel having 85% ethanol.As discussed below, ASTM D 5798 provides for variations in ethanolconcentration. One example is E70 containing 70% ethanol for thewintertime. The term E85 as used herein is intended to include any andall such variations.

The present invention is based on the findings as described herein thatblending commercially available gasoline meeting local volatilityrequirements with ethanol does not result in a fuel that meets theminimum vapor pressure limits of ASTM D 5798. The present inventioninvolves the inclusion of at least an amount of isopentane, or otherhigh volatility gasoline components such as n-pentane and butanes, inethanol or an ethanol-gasoline mixture that is sufficient to increasethe vapor pressure of the ethanol or ethanol-gasoline mixture to meetthe minimum vapor pressure limits of ASTM D 5798.

A vapor pressure program investigating the blending of E85 (a nominalblend of 85 vol % denatured ethanol and 15 vol % gasoline) wasundertaken to determine if using commercial gasoline meeting localvolatility specifications would result in E85 meeting the requirementsof ASTM D 5798 Specification for Fuel Ethanol (Ed75-Ed85) for AutomotiveSpark-ignition Engines.

Three commercial gasolines were used: CARBOB (California ReformulatedGasoline Blendstock for Oxygenate Blending) regular gasoline with 5.7psi vapor pressure, a premium gasoline with 8.7 psi vapor pressure, anda winter grade gasoline with 12.2 psi vapor pressure.

Each of the three commercial gasolines was blended at 15 vol % withdenatured ethanol to make E85. One-third and two-thirds of each of thegasoline portions were replace by isopentane resulting in six moreblends. Another blend was made using 15 vol % of isopentane (nogasoline). Finally, for winter blending D 5798 allows up to 30 vol %gasoline. So, a 30 vol % blend was made using the 12.2 psi gasoline. Thecompositions of the blends are shown in Table 1 TABLE 1 E-85 VAPORPRESSURE TEST PROGRAM BLENDS mL of Blending Stock Blend 8.7 12.2 DVPENumber Ethanol Isopentane CARBOB psi VP psi VP psi 1 1000 0 0 0 0 2.41 20 0 1000 0 0 5.67 3 0 0 0 1000 0 8.66 4 0 0 0 0 1000 12.18 5 850 0 150 00 4.44 6 850 50 100 0 0 6.45 7 850 100 50 0 0 8.51 8 850 150 0 0 0 10.859 850 0 0 150 0 4.73 10 850 50 0 100 0 6.63 11 850 100 0 50 0 8.51 12850 0 0 0 150 6.32 13 850 50 0 0 100 7.86 14 850 100 0 0 50 9.12 15 7000 0 0 300 8.26Vapor Pressure Testing

The vapor pressure of the blends was determined by ASTM D 5191. Thevapor pressure values reported were single determinations.

The vapor pressure results for the blending stocks (Blends 1 through 4)and for the ethanol blends (Blends 4 through 15) are shown in Table 1.

The effect on vapor pressure of adding the three commercial gasolinesand isopentane at 15 vol % to denatured ethanol and on adding 30 vol %of the 12.2 psi gasoline are shown graphically in FIG. 1.

The three ASTM D 5798 minimum vapor pressure class limits are plotted onFIG. 1 and show that when commercial gasolines meeting the federalsummertime vapor pressure limits of 7.8 and 9.0 psi maximum are blendedwith denatured ethanol, the resulting E85 blend will not meet theminimum vapor pressure limits. Using the winter gasoline which is notnormally available in the summertime resulted in complying only with thesummertime Class 1 minimum limit and not complying with the transitionmonths and the wintertime limits of Class 2 or Class 3. Even adding 30vol % of the 12.2 psi gasoline didn't result in E85 that complied withthe wintertime specification. Isopentane alone at 15 vol % provided avapor pressure of 10.85 psi which readily met the winter minimum limit.

The effects of replacing portions (one-third and two thirds) of the 15vol % gasoline with isopentane are shown graphically in FIG. 2 for eachof the three commercial gasolines.

Replacing a part of the gasoline portions with isopentane increased theresulting vapor pressure of E85. For summer gasolines it took about 3vol % isopentane of the 15 vol % total hydrocarbon portion to meetsummer standards. It took about 6.5 vol % isopentane to meet Class 2standards. For wintertime, it took about 11.5 vol % isopentane with the12.2 psi gasoline and about 12.3 vol % isopentane with the twosummertime gasolines to meet winter standards.

Predicting Vapor Pressure

There are two procedures for calculating the vapor pressure of blends.One is the linear method where the vol % of each blending component ismultiplied by its measured vapor pressure, summed across all components,and divided by 100. A more accurate way is to use Blending Indexes inplace of the measured vapor pressures. Both procedures were used tocalculate the vapor pressure of the E85 blends and the results are shownin FIG. 3.

For blending E85, the calculated vapor pressures by both methods arelower than the measured vapor pressure and the difference increases withincreasing vapor pressure. The Blending Index approach is slightlybetter than the linear approach, but probably not sufficiently better tojustify the use of the more complicated Blending Index method.Regression analyses were run using combinations of variables and thebest practical equation using vapor pressure data is as follows:E85 Vapor Pressure=−1.699+2.025*Calculated E85 VP+0.133*Vol %Isopentane, where the calculated E85 VP is determined using the linearmethod.Water Tolerance

Using isopentane to increase the vapor pressure of E85 resulted in anadditional unexpected benefit, a significant increase in the watertolerance of the fuel.

The water tolerance of the E85 made with 15 vol % CARBOB and the E85made with 15 vol % isopentane was assessed. The basic test for watertolerance of fuel is ASTM D 1094. The test method was modified for usein the field to detect and roughly quantify the ethanol content of E10(10 vol % ethanol blends) or of blends having lower ethanolconcentrations.

The basic procedure involves using a 100 mL graduated mixing cylinder.100 mL of gasoline-ethanol blend is placed in the graduated cylinder and10 mL of water is added. The graduate is shaken and time is allowed forthe water or water/ethanol phase to settle to the bottom. The increasein the volume of the water/ethanol bottoms is used to determine how muchethanol is present.

The situation is different for E85 in that water dissolves in theethanol and forces the gasoline out of solution (phase separation).Since gasoline is less dense than ethanol or water it floats to the topwhen phase separation occurs. To keep the proportions the same and stillbe able to measure the amount of separated gasoline, a 250 mL graduatedmixing cylinder was used for the E85 assessment.

When 10 mL of water was added to 100 mL of E85 made from CARBOB andshaken, the water dissolved into the E85 and the mixture remained clear.Additional water was added. When 16 mL water had been added, the mixturebecame hazy. It took more than 8 hours and less than 24 hours for thelower phase to clear. At this point 2 mL of gasoline was floating on thetop. A total of 20 mL of water produced 6 mL of phase separated gasolineand 30 mL of water resulted in 8 mL of gasoline separated from the E85.This finding shows that E85 is considerably more tolerant of watercontact than E10 which separates when about 0.5 mL water is added.

It was thought that with no aromatics present, the isopentane wouldseparate faster than the commercial gasoline. This was not the case. Nohaze or separation appeared until 40 mL of water was added. At thatpoint 13 mL of isopentane floated to the top and the fuel cleared of itshaze quickly. Thus, the isopentane-based E85 is more tolerant of waterthan the commercial gasoline-based E85.

There are numerous variations on the present invention which arepossible in light of the teachings and supporting examples describedherein. It is therefore understood that within the scope of thefollowing claims, the invention may be practiced otherwise than asspecifically described or exemplified herein.

1. An E85 fuel composition comprising ethanol, gasoline and isopentanepresent in amounts so that the fuel meets the applicable minimum vaporpressure limits of ASTM D
 5798. 2. A composition according to claim 1,comprising about 85 vol % ethanol, 12 vol % gasoline and about 3 vol %isopentane.
 3. A composition according to claim 1, comprising about 85vol % ethanol, 9 vol % gasoline and about 6 vol % isopentane.
 4. Acomposition according to claim 1, comprising about 85 vol % ethanol, 6vol % gasoline and about 9 vol % isopentane.
 5. A composition accordingto claim 1, wherein the gasoline is a commercially available gasoline.6. An E85 fuel composition having a sufficient quantity of addedisopentane to meet the applicable minimum vapor pressure limits of ASTMD
 5798. 7. A composition according to claim 6, comprising about 85 vol %ethanol and about 15 vol % isopentane.
 8. A composition according toclaim 6, comprising about 85 vol % ethanol, 12 vol % gasoline and about3 vol % isopentane.
 9. A composition according to claim 6, comprisingabout 85 vol % ethanol, 9 vol % gasoline and about 6 vol % isopentane.10. A composition according to claim 6, comprising about 85 vol %ethanol, 6 vol % gasoline and about 9 vol % isopentane.
 11. Acomposition according to claim 6, comprising about 85 vol % ethanol, 3vol % gasoline and about 12 vol % isopentane.
 12. A method for producingan E85 fuel composition comprising adding a sufficient quantity ofisopentane to ethanol or to a mixture of ethanol and gasoline which hasa vapor pressure lower than an applicable minimum vapor pressure limitof ASTM D 5798 to produce an E85 fuel having a vapor pressure thatcomplies with the applicable minimum vapor pressure limits of ASTM D5798.
 13. A method according to claim 12, wherein the gasoline is acommercially available gasoline.